As previously mentioned, it is preferable that the metallo-phthalocyanine compound of formula (I) have as a substituent a phenylthio group of the following formula (II) at one of the ??-positions of each benzene ring of the phthalocyanine skeleton: ##STR5## wherein R1 is an alkyl group having 1 to 4 carbon atoms or an alkoxyl group having 1 to 4 carbon atoms; and R2, R3, R4 and R5 each is an alkyl